Since the New Horizons Jupiter Encounter thread is already getting pretty long, I decided to create a thread dedicated to New Horizons' observations of the most interesting object in the solar system: Io. Info on upcoming observations comes from the jupiter_timeline_static.xls document john_s posted, and the preview images are from Celestia (note that each image is scaled so that the pixel scale is ~correct, and represents a smaller FOV than LORRI)

Today, February 24, New Horizons conducts three observations of Io with the LORRI camera as well some observations of Io's atmosphere with ALICE. These observations have the lowest phase angle for Io of the entire encounter. Phase angle continues to increase as NH approaches Jupiter and Io.

The first observation, ISunMon1, shows Io's sub-Jovian hemisphere (Clat=5.5 S, Clon=340.2 W) from a distance of 7,856,307 km. The resolution with LORRI would be 38.8 km/pixel. Pele is on the limb at lower right and Masubi is on the limb at lower left. Ra Patera is near center.

The second observation, ISunMon2, also shows Io's sub-Jovian hemisphere (Clat=5.5 S, Clon=15.1 W) from a distance of 7,575,510 km. The resolution with LORRI would be 37.5 km/pixel. The Tvashtar plume might be poking above the limb at upper left.

The third observation, ISunMon3, shows Io's leading hemisphere (Clat=6.0 S, Clon=84.7 W) from a distance of 6,627,459 km. The resolution with LORRI would be 32.8 km/pixel. The Zamama plume might be visible just above center on the left limb.

It only gets better from here. Not sure how NH downlink works, but there is a DSN window right after the last Io observation, hopefully at least one frame from each observation will be returned. Maybe they can do the Huffman window right around where Io is... Tomorrow contains four more observations of Io, highlighting Pele and an eclipse.

There was more excitement yesterday. We've been turning our Earthly (and near-Earthly) telescopes on the Jupiter system too, to give us the broader context for New Horizons' snapshot of the system. Yesterday Kandis Lea Jessup and I got our first look at the first Hubble pictures of Io, taken back on Valentine's Day (these were the images we had to scramble to redesign at the end of January, after the failure of Hubble's other camera). Io was only 16 pixels across in the pictures, but that was enough to show us something very interesting at ultraviolet wavelengths: there was a huge volcanic plume rising above the edge of Io's disk. We're not yet 100% sure which volcano is generating the plume, but I have a hunch that it's Tvashtar, a volcano that obliged Cassini by producing a similar-sized plume during Cassini's Jupiter flyby in late 2000. We've seen plumes like this in Hubble images before, but they aren't particularly common, so we are excited at the prospect of getting much closer images of this thing with New Horizons next week. In fact the New Horizons schedule includes a color image specifically to look at Tvashtar's plume, on the off-chance that there might be something there to see. We just need Tvashtar (or whatever volcano is actually responsible) to keep doing its stuff for one more week. Credit: John Spencer and Kandis Lea Jessup, Southwest Research Institute, and the Space Telescope Science Institute

Cool, certainly looks like it could be Tvashtar. Given the viewing geometry, there is a slightly better candidate in an unnamed patera at 61N, 143 W, but given that it was only seen as a hot spot once, Tvashtar would be the better candidate.

More Hubble images now down- the Tvashtar(?) plume continues to be active through at least February 22nd, so there's a good chance that it will be active during the flyby too. Hubble only sees the plume in the ultraviolet, so it's not a sure thing that we'll see it at longer wavelengths with New Horizons, but I think the chances are quite good, particularly after closest approach when high phase angles will make it more visible.

Not sure how NH downlink works, but there is a DSN window right after the last Io observation, hopefully at least one frame from each observation will be returned. Maybe they can do the Huffman window right around where Io is... Tomorrow contains four more observations of Io, highlighting Pele and an eclipse.

The only Io images we'll get down before the second week of March are ISunMon09, taken at 8:40 on 2/26, which will be sent down during the downlink immediately following on the 26th, and IHiRes05, taken at 11:00 on 2/28, which will come down during the downlink starting at 15:52 on 2/28. The limitation is as much the time needed to compress the images and prepare them for downlink, given how busy the spacecraft is, as the actual transmission time. Both will show the same hemisphere of Io, centered on longitude ~65, with Prometheus on the limb and Tvashtar also near the limb. I goofed slightly in selecting these two as our early downlink images, given their similar geometry, but there *were* a lot of constraints.

Today, February 25, New Horizons conducts three monitoring observations of Io with the LORRI camera focusing on the trailing hemisphere, as well some observations of Io's atmosphere with ALICE and an observation of Io while it is in eclipse with the LORRI, ALICE, and RALPH instruments. As noted in the post above, these observations won't be returned until next month.

Please keep in mind that these are simulations of the LORRI frames from Celestia, not the LORRI frames themselves...

The first observation, ISunMon5, shows Io's trailing hemisphere (Clat=3.0 S, Clon=225.4 W) from a distance of 5,276,976 km. The resolution with LORRI would be 26.1 km/pixel. Pele is visible at lower left and Prometheus is at center right. If Loki's plume(s) are active, then it *might* be visible at upper left.

The second observation, ISunMon6, shows Io's trailing hemisphere (Clat=3.0 S, Clon=253.1 W) from a distance of 5,217,587 km. The resolution with LORRI would be 25.8 km/pixel. Pele is now just below center and Loki has rotated into view at upper left. Prometheus' plume might be visible at center right, though as noted in the above posts, this might not be the best viewing geometry for observing Io's plumes given LORRI's wavelength range.

The third observation, ISunMon7, shows Io's trailing hemisphere (Clat=3.0 S, Clon=308.1 W) from a distance of 5,184,145 km. The resolution with LORRI would be 25.6 km/pixel. Pele is now visible at lower right. Loki is now visible near center. Not sure where Loki is in its geological clock, but the SNR of LORRI might be enough to allow one to see where the overturn front is in Loki Patera.

The final observation is Ieclipse1, an observation of Io in eclipse. RALPH will be active during the eclipse, allowing for an observation of Io's current volcanic activity. Loki should be easily visible in the LEISA images, depending again on where it is in its geological clock...

The only Io images we'll get down before the second week of March are ISunMon09, taken at 8:40 on 2/26, which will be sent down during the downlink immediately following on the 26th, and IHiRes05, taken at 11:00 on 2/28, which will come down during the downlink starting at 15:52 on 2/28. The limitation is as much the time needed to compress the images and prepare them for downlink, given how busy the spacecraft is, as the actual transmission time. Both will show the same hemisphere of Io, centered on longitude ~65, with Prometheus on the limb and Tvashtar also near the limb. I goofed slightly in selecting these two as our early downlink images, given their similar geometry, but there *were* a lot of constraints.

John.

Thanks for the inside look at the downlink. As always, the NH team is making us feel like real insiders.

What's the likely turnaround for these images to make it onto the SOC page? I remember things like the MER landings and Deep Impact where the first download images were just popping in right there on NASA TV but also situations like Huygens where there was a lot of stitching and sifting.

A little experiment on you guys- we posted the images about 40 minutes ago and were wondering how long it would take someone to notice them and spot the plume! We'll be doing a proper press release image in a few hours.

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